Machine tool



3 Sheets-Sheet l MACHINE 'I'OOL A; C. CARLSON Original Filed June 25,1941 INVENTOR.

ARTIE G. GARLSON ATTORNEY May 1, 1945.

y 1945- A. c. CARLSON 2,375,074

' MACHINE TOOL Original Filed June 23, 1941 3 Sheets-Sheet 3 FIG 3 m a?b v INVENTOR. ARTIE C.CARL$ON ,BY MM ATTORNEYS Patented May 1, 1945MACHINE TOOL Artie C; Carlson, Detroit, Mich, assignor to BremaccCorporation,

ration ofMichigan Detroit, Mich.,a corpo- Contlnuationot applicationSerial No. 399,381, June 23, 1941. 1This application January 5, 1944,Serial No. 517,139

13 Claims. This invention relates generally to machine tools andconstitutes a continuation of my applictaion filed June 23, 1941,bearing SerialNo. 399,361.,

More particularly, the invention relates to a nove1 feed mechanismapplicable generally to machine tools, but which is illustrated in thepresent case as applied to a milling machine.

One of the considerations which determines the accuracy and efiiciencyof machine tools, such for example as milling machines, is the abilityof the machine to traverse the table with a minimum of' vibration; Thisis particularly true in downcutting milling machines, in which my tablefeed is especially valuable. .According to the present invention, novelfeeding mechanism is employed which insures great rigidity of the tableand reduces vibration to a minimum. The ,feed is eflfected through apair of oppositely threaded feed screws cooperating with a pair ofoppositely threaded portions of a single feed nut, thefeed screws beingrespectively right and left hand, and rotated in opposite directions.Means are also provided for: efiecting a relative adjustment between thefeed screws so as to take up any looseness or backlash and to 'insure asmooth vibrationless feeding movement of the table.

' As a specifically difierent embodiment of the present invention thefeeding mechanism may comprise a pair of rigidly mounted feed screwshaving a rotatable feed nut associated with each screw. The feed nutsmay be geared together for simultaneous rotation, either in the same oropposite directions. A relative axial adjustment between one of the feedscrews and its corresponding feed nut is provided to take up backlash.

It is accordingly an object of the present invention to provide improvedfeeding mechanism for machine tools.

More specifically it is an object of the present invention to provideimproved feeding mechanism employing a plurality of parallel sets ofnutfeed screw elements in which means are provided for effecting alongitudinal adjustment between the elements of one set. 4

It is a further object of the present invention to provide novel feedingmechanism for machine tools in which a pair of oppositely threaded feedscrews cooperate with a pair of oppositely threaded portions of asinglegfe'ed nut.

v It is a further object of the invention to. provide novel feedingmechanism for machine tools in which a pair of oppositely rotated rightand left hand feed screws are provided, in association with a pair ofoppositely threaded portions of. a

single feed nut, and in which means areprovided for effecting a veryfine relativeladjustment between the feed screws;

Other objects of the invention will be apparent as the descriptionproceeds, and when taken in conjunction with the accompanying drawings,wherein: l I it Figure 1 is a plan view of the table provided withfeeding mechanism in accordance withthe present invention;

Figure 2 isa section on-the line 2-2, Figural, with parts broken away;

Figure 3 is a section on the line 3-3, Figure '2; Figure 4 is a sectionon the line 4-4, Figure 2; Figure 5 is a side elevation, with partsbrolren away, of a modified form of my improved feeding mechanism; and

Figure 6 is a section on the line 6--6, Figure 5. According to thepresentinventiona table ill is mounted for movement over a stationarybed i2. As usual, the table i0 is provided with a plurality of T-slots Il, by means of which a work piece may be secured thereto. As shown inFigure 3, a' groove [3 is provided around the periphery of the table Illand terminates in a spout for discharge of coolant and chipstoareceptacle ll formedas a part of the bed l2.

The bed l2 carries a longitudinally extending guideway 14 that has a:key l9 seated in a corresponding groove I911 in the bed l2 and is boltedor otherwise secured to the bed as indicated at It in Figure 4.Preferably the guideway 14 has inclined guiding surfaces l8 and 20respectively.

In the present instance the surface It is inclined at an angle ofapproximately 30 to'the horizontal, while the surface 2|! is inclined atan angle of 45 to the horizontal. This construction is desirable sinceit contributes to the accurate guiding of the table 10' initslo'ngitudinai mov ment.

The table I II has a gib 22 whichextends beneath a laterally projectingportion of the'guideway it and serves to" hold the table down onto theguideway" M. The table I0 is provided with accurately formed surfacescooperating with the surfaces [8 and '20 previously described to effectaccurate guided movement of the table I0. 1

At i'tsopposite side t e table leis provided with a laterally projectingrib 24 having an upper inclined surface 25, Mounted onthe bed Iris a gib28 having a surface 28a shaped to correspond to the surface 26. The gib28 is secured to the bed I2 by means of bolts 30 which pass throughenlarged openings 32 in the gib 28. This permits adjustment of the gib28 before it is rigidly clamped down by bolts 30. Fine lateraladjustment of the gib 28 is effected by means of an adjusting screw 34received in a tapped openma 36 in the bed I2.

The table I has a laterally projecting portion 38 which rests on the topof the adjustable gib 28. By adjusting the gib 28 laterally, the tableI0 may be firmly supported and held down while being guided by thesurfaces I8 and previously described.

As shown in Figure 4, the table I0 is provided with T-slots 40 and 42respectively formed in an inclined surface 44 for the reception ofconventional actuating elements or dogs 46 which cooperate with suitablecontrol mechanism -(not shown).

In order to efiect feed and traverse movement of the tablev I0, a sourceof power (not shown) is connected to a gear 48 splined upon a splineshaft 50. In Figure 2 I have shown a separate feed train housing 52 for.supporting the spline shaft .50 and other mechanism later to bedescribed. The housing 52.is bolted or otherwise secured to the bed I2by suitable means, or if preferred, it may be cast therewith as anintegral part.

A,laterally projecting portion 48a of the gear 48 is mounted in abearing 54 and is retained against axial movement relative thereto bynut 55. Bearing 54 is firmly held in the housing 52 by retainer ring 58bolted thereto as indicated at 51.

$pline shaft extends between and is carried by depending webs 58 and 59of the table I0. At the left, as seen in Figure 2, spline shaft 50 isprovided with a bearing 60 carried by web '58. At the other end, splineshaft 50 has a gear 88 key'ed'thereto. Preferably this gear 86 ispositionedbesidetheweb 59 and has a laterally projecting tubular portion86a mounted in" a bearing 6| carried by the web 59. Bearing BI isretained in web 59 bymeansof a plate 62 and a nut 63. Thus gear 88 ismounted for rotation beside-web 59 and is firmly held against axialmovement relative thereto. I

The table I0is also provided adjacent the web 59 with another dependingweb I0, and such webs provide therebetween a space 12. Other dependingwebs I3 and 13a of the table cooperate with the webs 59 and I0 and witha bottom closureplate I4 to form a transmission housing.

A pair of oppositely threaded feed screws I6 and 18 are provided for thetable I0 and extend through and are carried by webs 58, 59 and I0respectively. As shown in Figure 2, the feed screw I8 is provided in web58 with bearing which permits limited axial movement of the feed screwI8 therein. The feed screw 18 is further provided in web I0 with anadjusting structure indicated generally at 82 which will hereinafter bedescribed. i

' The feed screw I8 carries within an opening in the web 59 a laterallyextending tubular part 84a of a gear 84 which meshes with the gear 86.Preferably gear 84 is mounted for rotation on screw I8 which in turn ismounted in a bearing 85 in the web 59. Such gear 84 and the bearing 85therefor are held against axial movement relative to the web 59 by meansof-a retainer plate 64andnut8l.

The gear 84 also meshes with an identical gear 88 keyed to feed screwI6. Thus it will be apparent that gears 84 and 88 will rotate inopposite directions and will transmit opposite rotation to theircorresponding feed screws.

The feed screw I6 is carried by preloaded bearings I22 and I24 locatedin the webs 59 and I0 and designed to carry both radial and thrust loadsof the feed screw I6. The bearing I22 is located between a shoulder 11on screw I6 and a shoulder 59b of the web 59. A retainer I2I is boltedto the web 59 to hold the bearing I22 against axial movement relativethereto. The bearing I24 is located between a shoulder 10b of the web I0and a nut I23 on the screw I6. A spacer I25 is located between the gear88 and the bearing I24, while a retainer I29 is bolted to the web I0 tohold the bearing I24 against axial movement relative thereto. Thus thebearings I22 and I24, gear 88, spacer I25 and feed screw I6 constitute arotatable unit that is carried by but is effectively held against axialmovement relative to the table I0. I Y

The gear 84 is provided with an internal hardened and ground bore 90which permits the feed screw I8, which has a correspondingly finishedportion 92, to move therein.

For transmitting rotation of the gear 84 to the feed screw 18, a clutchor coupling element 94 is keyed or otherwise secured to the feed screwI8 and is provided with a tongue I02 for clutching engagement with aslot I00 in a laterally projecting tubular part or hub 98 of the gear84. Thus a driving relationship between the gear 84 and the clutchelement 94 on the feed screw I8 is maintained while the feed screw I8 ismoved axially relative to the gear 84.

A feed nut I04 is bolted or otherwise secured to the feedtrain housing52 as indicated generally at I06 and has a pair of oppositely threadedportions I04 and I04. It will be apparent that rotation of the feedscrews I8 and 18 in the threaded portions I04 and I84" of this nut I04will effect longitudinal movement of the table I0.

In order that the feed screws I6 and I8 may be relatively adjusted sothat they will cooperate properly with the feed nut I04, the followingmeans is provided for effecting slight adjustment of the feed screw I8longitudinally with respect to the table I0. The clutch element 94, aspreviously described, is keyed or otherwise rigidly secured to the feedscrews I8. Bearings I08 are rigidly assembled on clutch element 94 bynuts I09. The bearings I08, in turn, are mounted in an adjusting housingIII], and are assembled therewith by retainer ring III. The housing IIOis provided as indicated at II2 with threads, by means of which it maybe adjusted in opposite directions axially of the web I0 of the tableI0. Preferably the threads II2 are a fine pitch so that a very fineaxial adjustment of the feed screw 18 in opposite directions may thus beobtained. It will be understood that the bearings I08 when adjusted areeffective to bring about corresponding axial adjustment of the feedscrew I8.

Means are provided for locking the housing H0 in adjusted position andcomprises a looking element II4 having a projecting tang IIB adapted tobe received within a corresponding slot II8 formed in the periphery ofthe housing H0. The locking element H4 is fastened to the table I0 by abolt I28,'and a plurality of slots II8are provided around the peripheryof the housingfor the reception of the tang H6.-

2,375,074 Withthe foregoing structure in mind, the

operation of the mechanism will be briefly :de

scribed Feed screws 16 and 18 will engage with the fed nut I04.- Feedscrew 16 is carried by but is rigidly supported against axial movementrelative to the table I0. Feed screw 18-is also carried-by the table Iand is adjusted in opposite directionsby means of the adjusting mecha--nism,indicated generally at 82, including the housing I I0, so that aproper relationship-exists between feed screws 16 and 18 and the feednut I84. It will be appreciated that by virtue of the adjustment of thefeed screw 18 in opposite directions it will be possible to eliminatesubstantially all backlashand loosenessin thedriving connection, at thesame time to prevent binding of the parts. I 1

Power from any suitablesource istransmitted to the gear 48 by means of adrive gear (not shown), Due to the spline connection between the gear 48and the spline shaft 50, the shaft 50 is rotated, thereby rotating thegear 86. Rotationof the gear 86 results in corresponding rotation of thegear 84 which, in turn, drives the coupling element 94 through thetongue I02 formed thereon and the slot I00 formed in the hub 98 of thegear 84. In this connection it will be noted that the relation of thetongue I02 and slot I00 is such that the proper clutching relation ismaintained during adjustment of the housing IIll relative to the web 10of the table. Rotation of the clutch element 94 is imparted to the feedscrew 18, At the same time, rotation of the gear 84 results incorresponding rotation in a reverse direction of the gear 88; The gear88 is keyed to feed screw 16, and accordingly feed screws 16 and 18willrotate' at equal speeds in opposite directions in thethreadedportions I04 8 and I04 of the feed nut I84 that is fixed relative to thebed I2. Since the feed screws 16 and 18 are of opposite hand, theirrotation inopposite directions cooperates to produce a feeding movementof the table ID on the bed I2.

Referring now to Figures and 6, I have illustrated a modification of myinvention wherein the operating principle is the same, but therelationship between the feed screws and feed nuts is reversed. r n

In these figures I have illustrated a bed I50 on which the table I5I ismounted for reciprocation. Suitable ways, which may be like those shownin Figures 3 and 4, are provided.

The feed nuts I53 are mounted for secured against axial movementrelative thereto. 1

For this purpose nuts I53 are provided with shoulders I54, against whichbearings I55 areretained as by means of the lock nuts I56. Bearings I55are rigidly supported in the brackets I52 by retainer plates I 51 boltedor otherwise secured thereto. I

-At the opposite end of nuts I53 I provide bearings I58 rigidlyassembled thereon by means of lock nuts I59 and spacers IGO. BearingsI58 are retained in right-hand bracket I52, as seen in Figure 6, bymeans of retainer plates I6I bolted'or otherwise rigidly securedthereto.

1 The nuts (I53 are each provided with a gear 162, keyed: thereto asindicated at I63, and the ders 1I54 through the spacers I60, bearingsI58 and nuts I59. By thisconstructionthe feed nuts I53 are both firmlyretained against axial shifting while being mounted for substantiallyfree rotation.

The gears I62'are identical, so that when one of. said gears I62 isdriven the other gear I62 will be driven thereby in the oppositedirection at the same speed. :The table I5! has webs I65 at oppositeends thereof between which are supported the feed screws I 66 and I61.As shown in Figure 6, the feed screw I66 is right-hand and feed screwI61 is.=1efthand. It will be appreciated that the feed nuts I53cooperating therewith are formed with threads adapted to cooperate, withthe threads formed on the corresponding feed screws. The feed screws I66and I61 are supported. against rotation at their left-hand end, asseenin Figure 6, by elements I68 which have splined connections with theends of the feed screws, as indicated at I69. Elements I68 are seated inopenings in the web I65 and are retained therein against rotation bysuitable securing means, such as the bolts indicated at I10. One of thefeed screws, as for example the right-handfeed screw. I66 is rigidlysupported between the webs I65, and for this purpose is provided with anintegral collar Ill and a threaded endiportion I12 on which is' aclamping nut 113. The feed screw I66 is thus rigidlygsupported againstaxial movement by the clamping action between collar HI and the nut I13.

The other feed screw I 61 is mounted for limited axial adjustmentwithout rotation, and for this purpose is provided with a collar I15 anda threaded end portion I16. An adjusting element I11 is threadedwithinan opening I18 formed in the right-hand web I65 of the table I5I.Preferably the threads onthe adjusting element I11 are of fine pitch sothat avery fine adjustment may be effected by rotation ofthe adjustingelement I11. I The adjusting element I11 is adapted to be locked inadjusted position by a locking member I86, which may be identical withthe locking element II4 shown in Figure 2. Theadjusting elementI11 has arecess I8I into which the threaded end I16 oi the feed screw-extends.

A clampingnut I82 and a locking nut I83 are threaded on the end I16 ofthe feed screw, and

are adapted to retain the feed screw I61 against axial displacementrelative to the adjusting element I11. 7

In order to effect adjustment of the feed screw 161, nuts I82 and I83are loosened and the adjusting element I11 is then rotated in thethreaded opening I18 to effect axial displacement thereof. When it hasbeen properly located, nuts I82 feed nuts I53, as will be evident. Thegear I 85 is-driven from any suitable feed mechanism, such forexampleasa motor and a train of gearing.

While the two embodiments of my invention illustrated and described inthe foregoing show a righthand and a left-hand feed screw and a feed nutcombination, it will be apparent that the same result can be obtained byemploying a feed screw-feed nut combination, both of which are of thesame hand. If the combinations are of the same hand, an idler gear willbe interposed between the gears interconnecting the feed screws forrotation, as shown in Figures 1 to 4, or between the gearsinterconnecting the feed nuts for rotation, as disclosed in Figures 5and 6. The effect of the idler gear, as will be obvious, is to providerotation of the same hand to the rotatable feed screw or feed nutelement. In all cases, of course, the feed nuts and feed screws are ofthe same pitch.

Since my invention is primarily in the feeding mechanism for a table, Ihave not shown a complete machine, and it will be understood that theinvention is applicable to machine tools generally where it is desiredto effect the uniform and smooth translation of a table or carriage.

While I have illustrated and described two preferred forms of feedingmechanism, it will be appreciated that this has been done solely toenable those skilled in the art to practice the present invention, thescope of which is indicated by the appended claims.

What I claim as my invention is:

1. In a machine tool, a movable work carrier, a support for saidcarrier, and mechanism for moving the carrier over said support,including a feed nut having a :pair of oppositely threaded portions, andcarried by and axially immovable relative to said support, a rotatablegear carried by and axially immovable relative to said support, a splineshaft movable with the carrier and extending axially through the gear tobe rotated thereby, a pair of oppositely threaded feed screws movablewith the carrier in substantially parallel relation to said spline shaftand engaging said threaded portions of the feed nut whereby rotation ofsaid feed screws relative to said nut imparts movement to the carrier,and means for driving the feed screws from said spline shaft.

2. In a machine tool, a movable Work table, a bed for supporting saidtable,'and mechanism for moving the table over said bed, including afeed nut rigid with said bed and having a pair of oppositely threadedportions, a gear rotatably mounted upon said bed and axially immovable,a spline shaft carried by and movable with the table and extendingaxially through the gear to be rotated thereby, a pair of oppositelythreaded feed screws carried by and movable with the table insubstantially parallel relation to said spline shaft and engaging saidthreaded portions of the feed nut whereby rotation of said feed screwsrelative to said nut imparts movement to the table, and means includinga single gear train for driving the feed screws from said spline shaft.

3. In a machine tool, a movable Work carrier, a support for saidcarrier, and mechanism for moving the carrier over said support,including a feed nut having a pair of oppositely threaded portions andcarried by and axially immovable relative to said support, a rotatablegear carried by and axially immovable relative to said support, a splineshaft movable with the carrier and extending axially through the gear tobe rotated thereby, a pair of oppositely threaded feed screws movablewith the carrier in substantially parallel relation to said spline shaftand engaging said threaded portions of the feed nut whereby rotation ofsaid feed screws relative to said nut imparts movement to the carrier,means for driving the feed screws from said spline shaft, and means onone of said feed screws adjustable relative to said carrier to take upbacklash in said feed screw.

4. In a machine tool, a movable work carrier, a support for saidcarrier, and mechanism for moving the carrier over said support,including a feed nut having a pair of oppositely threaded portions andcarried by and axially immovable relative to said support, a rotatablegear carried by and axially immovable relative to said support, a splineshaft movable with the carrier and extending axially through the gear tobe rotated thereby, a pair of oppositely threaded feed screws movablewith the carrier in substantially parallel relation to said spline shaftand engaging said threaded portions of the feed nut whereby rotation ofsaid feed screws relative to said nut imparts movement to the carrier,means for driving the feed screws from said spline shaft, and means foreffecting a relative adjustment between the feed screws to take uplooseness and backlash.

5. In a machine tool, a movable work carrier, a support for saidcarrier, and mechanism for moving the carrier over said support,including a feed nut having a pair of threaded portions and carried byand axially immovable relative to said support, a rotatable gear carriedby and axially immovable relative to said support, a spline shaftmovable with the carrier and extending axially through the gear to berotated thereby, a pair of threaded feed screws movable with the carrierin substantially parallel relation to said spline shaft and engagingsaid threaded portions of the feed nut whereby rotation of said feedscrews relative to said nut imparts movement to the carrier, means fordriving the feed screws from said spline shaft, and means carried by thecarrier and operable relative thereto to adjust one of the feed screwsin opposite directions to take up backlash.

6. In a machine tool, a movable work table, a

support for said table, and mechanism for moving the table over saidsupport, including a feed nut having a pair of oppositely threadedportions and carried by and axially immovable relative to said support,a rotatable gear carried by and axially immovable relative to saidsupport, a spline shaft carried by and movable with said table, saidspline shaft extending axially through the gear to be rotated thereby, apair of oppositely threaded feed screws carried by and movable with thetable in substantially parallel relation to said spline shaft, said feedscrews engaging said threaded portions of the feed nut whereby rotationof said feed screws relative to said nut imparts movement to the table,a gear free upon one of said feed screws, a gear on the spline shaftmeshing with the free gear to drive the same, a gear on the second feedscrew meshing with and operable by the free gear to drive said secondfeed screw, and means including cooperating clutch elements on the firstmentioned feed screw for driving the first feed screw from the freegear.

7. In a machine tool, a movable work table, a support for said table,and mechanism for moving the table over said support, including a feednut having a pair of threaded portions and carried by and axiallyimmovable relative to said support, a rotatable gear carried by andaxially immovable relative to said support, a spline shaft carried byand movable with said table, said spline shaft extending axially throughthe gear to be rotated thereby, a pair of threaded feed screws carriedby and movable with the table in substantially parallel relation to saidspline shaft, said feed screws engaging said threaded portions of thefeed'inutwhereby rotation of said feed screws relative to saidnutimpartsmovement to the tablaa? gear freeuponone of said feed screws, a'gear onthe spline shaft meshing with the free gearttc driye the same, :a gearon the second feed screw meshing with and operable by the free gear todrive said second feed screw, means including cooperating clutchelements on the first mentioned feed screw for driving the first feedscrew from the free gear, and adjustable means carried by the table foradjusting the first feed screw axially in opposite directions totake upbacklash, the cooperating clutch elements being constructed and arrangedwhereby the driving,

connection between the free gear and first mentioned feed screw ismaintained during adjust-,

ment of the first feed screw by the adjustable means aforesaid.

8. In a machine tool, a movable work table, a support for said table,and mechanism for moving the table over said support including a feednut having a pair of oppositely threaded portions and carried by andaxially immovable relative to said support, a bearing carried by andaxially immovable relative to said support, a rotatable gear having asupporting portion extending through and axially immovable relative tosaid bearing, a spline shaft carried by and movable with the table, saidspline shaft extending axially through the gear to be rotated thereby, apair of oppositely threaded feed screws carried by and movable with thetable in substantially parallel relation to said spline shaft, said feedscrews engaging said threaded portions of the feed nut whereby rotationof said feed screws relative to said nut imparts movement to the table,and means for driving the feed screws from said spline shaft.

9. In a machine tool, a movable table, a support therefor, and means formoving the table over said support, including a rotatable splined shaftcarried by and movable with the table, a

' drive gear splined upon said shaft and operable to rotate the same,said drive gear being carried by and axially immovable relative to saidsupport, a second gear upon said shaft to be rotated thereby, a pair ofsubstantially parallel threaded feed screw carried by and movable withthe table in substantially parallel relation to said splined shaft, oneof said feed screws being adjustable axially in opposite directionsrelative to said table to take up backlash, meshing gears on said feedscrews, one being secured to one of said feed screws, and the otherbeing free upon the other of said feed screws and meshing with thesecond gear aforesaid to be driven thereby, a

clutch for establishing a driving connection between the free gear andthe feed screw upon which it is mounted, said clutch being operable tomaintain such driving connection during axial adjustment of theadjustable screw, and a feed nut rigid with the support and having apair of threaded portions engaged by said feed screws whereby rotationof said feed screws relative to said nut imparts movement to the tablerelative to the support.

10. In a machine tool, a movable table, a support therefor, and meansfor moving the table over said support, including a rotatable splinedshaft carried by and movable with the table, a drive gear splined uponsaid shaft and operable to rotate the same, said drive gear beingcarried by and axially immovable relative to said support, a second gearupon said shaft to be rotated thereby, a pair of substantially parallelthreaded feed screws carried by and movablewith the table insubstantially parallel relation to said splined shaft fone of saidfeedscrew being adjustable axially in opposite directions relative to saidtable to take up backlash, meshing gears on said feed screws, one beingsecured to one of said feed screws, and the other being free upon theother of saidfeed screws: and meshing with the second gear aforesaid tobe driven thereby, a clutch for establishing a driving connectionbetween the free gear and the feed screw upon which it is mounted, saidclutch being operable to maintain such driving connection during axialadjustment of the adjustable feed screw, a feed nut rigid with thesupport and having a pair of threaded portions engaged by said feedscrews whereby rotation of said feed screws relative to said nut impartsmovement to the table relative to the support, and means forsynchronizing movement of said feed screws, including means carried bysaid table for adjusting axially in opposite directions the axiallyadjustable feed screw relative to said table.

11. In a machine tool, a movabletable, a support therefor, and'means formoving the table over said support, including a rotatable splined shaftcarried by and movable with the table, a drive gear splined upon saidshaft and operable to rotate the same, said drive gear being carried byand axially immovable relative to said support, a second gear upon saidshaft to be rotated thereby, a pair 'of substantially parallel threadedfeed screws carried by and movable with the table in substantiallyparallel relation to said splined shaft, one of said feed screws beingadjustable axially in opposite directions relative to said table to takeup backlash, meshing gears on said feed screws, one being secured to oneof said feed screws, and the other being free upon the other of saidfeed screws and meshing with the second gear aforesaid to be driventhereby, a clutch for establishing a driving connection between the freegear and the feed screw upon which it is mounted, said clutch beingoperable to maintain such driving connection during axial adjustment ofthe adjustable feed screw, a feed nut rigid with thesupport and having apair of threaded portions engaged by said feed screws whereby rotationof said feed screws relative to said nut imparts movement to the tablerelative to the support, means for synchronizing movement of said feedscrews, including means carried by said tablefor adjusting axially inopposit'e directions the axially adjustable feed screw relative to saidtable, and means carried by the table for locking the adjusting means inadjusted position.

12. In feeding mechanism of the character described, a support, a feedscrew, a gear loosely mounted on said feed screw, means mounting saidgear on said support for rotation only, means scribed-a support, a feedscrew, a gear loosely mounted on said feed screw, mean mounting saidgear on said support for rotation only, means mounting said feed screwon said support for rotation and for limited axial movement, a drivingcoupling rigidly secured to said feed screw having portions engageableby said gear throughout a range of relative axial adjustmenttherebetween, a bearing rigidly retained against axial movement on saidcoupling, a bearing housing in which said bearing is rigidly retainedagainst axial movement, said support having an internally threadedopening aligned with said feed screw, said housing being externallythreaded and adjustably positioned in said opening to effect axialadjustment of said feed screw.

ARTIE C. CARLSON.

